The subject matter described herein relates generally to a renewable power generation system and, more particularly, to methods and system for operating a renewable power generation system to provide power to a load.
Renewable power generation systems, for example, wind and solar energy generation systems, offer the advantages of being relatively safe and reliable. Moreover, such technologies have the common advantage of drawing power from sources that are virtually inexhaustible. However, the underlying energy sources such as wind and sunlight, may be subject to periodic swings in availability, such as, for example, varying winds, and/or varying weather patterns that can affect the amount of sunshine received each day.
At least some known wind energy generation systems include one or more wind turbine generators having a rotor with multiple blades. The rotor is sometimes coupled to a housing, or nacelle, that is positioned on top of a base, for example, a truss or tubular tower. At least some known utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) have rotor blades having predetermined shapes and dimensions. The rotor blades transform mechanical wind energy into induced blade lift forces that further induce a mechanical rotational torque that drives one or more generators, subsequently generating electric power. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into the electric utility grid. Gearless direct drive wind turbine generators also exist.
Typically, wind energy follows a diurnal cycle and annual cycle, wherein the wind speed is generally higher during the night and the winter season, as opposed to during the day and the summer season. While the wind energy is typically more abundant during the night and the winter season, electricity demand during such periods is generally lower than the electricity demand during the day and the summer season. As a result, generally, a wind farm generates more electricity during time periods when there is a lower demand for electricity.
Traditionally, renewable power generation systems rely on utility grids for transferring the generated energy to where it will be used. This may not be the most efficient use of the generated energy from an economic standpoint. As is well known, connecting a wind turbine generator to a utility grid imposes certain constraints on the generator. For example, the power output of the generator must be synchronized with the utility grid supply. When synchronizing generators, the rotor speed of the turbine is controlled to exactly match the utility supply frequency. Another constraint with relying solely on a utility grid as the carrier of generated energy is that there may be a low demand on the grid during the same time periods that there is ample capacity to generate additional power. When this occurs, the energy that could be captured is simply wasted. Although various energy storage systems, such as battery storage systems, can be utilized, such storage systems are relatively expensive and have efficiency losses of their own due to the repeated energy conversions, such that the benefits are outweighed by the costs.
The intermittent nature and variable speed of wind are drawbacks of wind generation systems, which may result in reduced system availability and reduced penetration. One popular way to store wind energy is using a small hydro plant to pump water to a higher reservoir. However, this requires special geological features and a large investment. There is a need to efficiently use and/or store the electricity generated by a wind farm during these low demand and “off-peak” times. Existing solutions to the intermittency problem of wind power generation devices, such as through the use of energy storage systems, have traditionally either been cost prohibitive or have low energy efficiency. Another way to mitigate intermittency and increase system availability is to use wind generation in parallel with other generating sources, which can be complimentary to the wind. However, such systems are also expensive.